1. Field of the Invention
Embodiments of the present invention generally relate to chemical mechanical polishing of substrates, and more particularly to a carrier head for use in chemical mechanical polishing.
2. Description of the Related Art
In the semiconductor manufacturing industry, planarization is a process of removing material from a substrate for smoothing a surface of the substrate, thinning an exposed layer, or exposing layers beneath the surface of the substrate. Substrates typically undergo planarization after one or more deposition processes builds layers of material on the substrate. In one such process, openings are formed in a field region of the substrate and filled with metal by a plating process such as electroplating. The metal fills the openings to create features, such as wires or contacts, in the surface. Although it is desired that the openings be filled with metal only to the level of the surrounding substrate, deposition occurs on the field region as well as the openings. This extra unwanted deposition must be removed, and planarization is the method of choice for removing the excess metal.
Chemical Mechanical Planarization (CMP) is one of the more common types of planarization processes. A substrate is mounted on a carrier head or polishing head and scrubbed with an abrasive pad or web. The substrate may be rotated against a web as the web is translated linearly beneath the substrate, or the substrate may be rotated against a pad while the pad is also rotated in the same or opposite direction, translated linearly, translated in a circular motion, or any combination of these. An abrasive composition is frequently added to the scrubbing pad to accelerate material removal. The composition typically contains abrasive materials to scour the substrate, and chemicals to dissolve material from the substrate surface. In the case of Electro-Chemical Mechanical Planarization, a voltage is also applied to the substrate to accelerate removal of material by electrochemical means.
Some carrier heads include a flexible membrane with a mounting surface that receives a substrate. A chamber behind the flexible membrane is pressurized to cause the membrane to expand outwardly and apply a load to the substrate. Many carrier heads also include a retaining ring that surrounds the substrate, e.g., to hold the substrate in the carrier head beneath the flexible membrane. Some carrier heads include multiple chambers to provide different pressures to different regions of the substrate.
An objective of CMP is to remove a predictable amount of material while achieving uniform surface topography both within each wafer and from wafer to wafer when performing a polishing process.
Therefore, there is a need for improved methods and apparatus for polishing substrates.